Python API: Expose background drawing as argument for gpu.types.GPUOffScreen.draw_view3d() #105748

Yuntoko · 2023-03-14T01:00:13+01:00

Yuntoko commented

2023-03-14 01:00:13 +01:00

Currently, when using the python api for offscreen drawing, the default background will always be rendered into the GPUOffScreen's framebuffer, rendering the alpha channel essentially useless and making it difficult to separate objects from the background.

This patch allows offscreen drawing of a 3d view with transparent background by exposing an optional parameter to the python api, enabling, for example, compositing the result over another image.

The new parameter to draw_view3d() is optional, with the default value matching the previous behavior, so this change is fully backwards-compatible.

offscreen.draw_view3d(
        scene,
        context.view_layer,
        context.space_data,
        context.region,
        view_matrix,
        projection_matrix,
        do_color_management=False,
        draw_background=False) # New optional keyword parameter

Currently, when using the python api for offscreen drawing, the default background will always be rendered into the GPUOffScreen's framebuffer, rendering the alpha channel essentially useless and making it difficult to separate objects from the background. This patch allows offscreen drawing of a 3d view with transparent background by exposing an optional parameter to the python api, enabling, for example, compositing the result over another image. The new parameter to draw_view3d() is optional, with the default value matching the previous behavior, so this change is fully backwards-compatible. ----- ``` offscreen.draw_view3d( scene, context.view_layer, context.space_data, context.region, view_matrix, projection_matrix, do_color_management=False, draw_background=False) # New optional keyword parameter ```

test-draw-background-pyapi.blend

861 KiB

screenshot.png

705 KiB

Yuntoko added 1 commit 2023-03-14 01:00:23 +01:00

buildbot/vexp-code-patch-coordinator Build done. Details

d1438add40 Python API: Expose background drawing as argument for gpu.types.GPUOffScreen.draw_view3d()

Currently, when using the python api for offscreen drawing, the default background will always be rendered into the GPUOffScreen's framebuffer, rendering the alpha channel essentially useless and making it difficult to separate objects from the background.

This patch allows offscreen drawing of a 3d view with transparent background by exposing an optional parameter to the python api, enabling, for example, compositing the result over another image.

The new parameter to draw_view3d() is optional, with the default value matching the previous behavior, so this change is fully backwards-compatible.

Brecht Van Lommel requested review from Jeroen Bakker 2023-04-05 18:09:41 +02:00

Brecht Van Lommel requested review from Germano Cavalcante 2023-04-05 18:09:41 +02:00

Germano Cavalcante commented

2023-04-05 18:33:46 +02:00

This function is old, I'm not familiar with the draw_background parameter.
If enabled, does it reuse the current offscreen color slot?
If that's the case, I think the parameter name could be "clear_color=True".

But I'm still not sure of the motivation for this change. Isn't it better to avoid adding more parameters to draw_view3d in order to simplify the API? Why not simply redraw the result with alpha over an background texture?

This function is old, I'm not familiar with the draw_background parameter. If enabled, does it reuse the current offscreen color slot? If that's the case, I think the parameter name could be "clear_color=True". But I'm still not sure of the motivation for this change. Isn't it better to avoid adding more parameters to `draw_view3d` in order to simplify the API? Why not simply redraw the result with alpha over an background texture?

Jeroen Bakker commented

2023-04-06 08:21:09 +02:00

the draw_view3d is a legacy function. And when the background is drawn the transparency data isn't available to do the compositing. The background actually is drawn with an alpha under replacing all alpha values.

Yes we should make a new API for offscreen rendering that would be more configurable currently it isn't clear how this will look like. The new API would also consider overlays etc. I am fine to add this optional parameter for now.

Usecase is same as for other cases where draw_view3d is used, mostly for automation in pipelines where speed is desired or where compositing isn't executed in Blender.

the draw_view3d is a legacy function. And when the background is drawn the transparency data isn't available to do the compositing. The background actually is drawn with an alpha under replacing all alpha values. Yes we should make a new API for offscreen rendering that would be more configurable currently it isn't clear how this will look like. The new API would also consider overlays etc. I am fine to add this optional parameter for now. Usecase is same as for other cases where draw_view3d is used, mostly for automation in pipelines where speed is desired or where compositing isn't executed in Blender.

Germano Cavalcante approved these changes 2023-04-06 15:22:31 +02:00

source/blender/python/gpu/gpu_py_offscreen.c Outdated

						
				@ -304,2 +304,3 @@

				    "   :arg do_color_management: Color manage the output.\n"

				    "   :type do_color_management: bool\n");

				    "   :type do_color_management: bool\n"

				    "   :arg draw_background: Draw background.\n"